Helsinki Day began to be celebrated at the Helsinki Society's proposal with the help of Mayor Lauri Aho in 1959, when Helsinki turned 409 years old. The date of 12 June was not defined as Helsinki's birthday until 1950, when Helsinki celebrated its 400th anniversary. In fact, the establishment of the city had been planned since 1547, and the king gave the order for the establishment of the city on 1 February 1550. The king's order on 12 June 1550, which ordered bourgeoisie from Rauma, Ulvila, Ekenäs and Porvoo to move to the new city of Helsinki, was better suited to the Finnish historical image and, of course, June was well suited for celebrations.
The programme of the first Helsinki Day included outdoor concerts and visits to city offices and institutions. In 1960, having celebrated Helsinki Day twice, the City Board decided that Helsinki Day would become an annual event. The events of Helsinki Day were popular, and in 1961 it was estimated that 8,000 city residents participated in the event.
Initially, the event programme was decided by the city board. Since then, the city's agencies and institutions have decided on the program on their own, together with associations and other private actors. Nowadays, the Helsinki Day programme is coordinated by the Helsinki Event Foundation. Helsinki Day was a piece of news and at the same time a great way to share the day's programme. In 1981, Ilta-Sanomat wrote: "IS tells can tell you today how Helsinki celebrates tomorrow".
This historic day has always been one to highlight current events. In 1965, the foundation stone of the City Theatre was solemnly laid down on Helsinki Day, and in 1979, three years before the start of the metro service, 8,000 lucky residents got to explore a metro car on Helsinki Day. In 1963, a mailbox was opened for “complaints”, as the matter was titled in Helsingin Sanomat. That is, the city residents had the opportunity to express their wishes to the city. And they did pile up in great number, up to 400 initiatives in 1963. Some of the initiatives produced results, including a bus stop at the beginning of Vihdintie and street lights in the Castrén Park behind the Kallio rescue station. By the 1970s, the number of citizens' initiatives decreased, but residential participation was encouraged, for example, by the City Museum seeking photographs from the residents.
In addition to open house events, the longest-standing tradition is the mayor's morning coffee at City Hall, which can be attended by anyone. As a newer tradition, the mayor's morning coffee is also celebrated at kindergartens and at playgrounds during park dining. Since 1996, Stadin Slangi ry has annually nominated the Stadin Friidu and Stadin Kundi, an award for the year’s most jovial man and woman. Since 2013, apart from during COVID, the entire city has been able to enjoy a picnic on the Esplanade.
Helsinki Day is for everyone in the city, everywhere in the city. Although the editor of Hufvudstadsbladet suspected in 1964 that the celebration of Helsinki Day would lose its meaning due to people moving to the suburbs, the celebration expanded to suburbs early on. In 1968, the main celebration of Helsinki Day was at Pirkkola Sports Park. Nature has been a highlight in the themes of Helsinki Day, such as "Helsinki, the city of the sea and islands" in 1967, "Helsinki is green" in 1968, and "Helsinki, the city of parks" in 1982. Suitable for the summertime, many of the Helsinki Day events are held outside. In 1977, the theme of Helsinki Day was Helsinki Outdoors and a track suit was proposed as the party outfit.
Although the day is not an official flag day, it was celebrated with hoisting the flag as early as 1963. On this day, the city commemorates distinguished residents with the Helsinki Medal, which is awarded by the City Board. At first, it was granted only on merit for the benefit of the city, then also for 30 years of service to the City of Helsinki. There is also a particular person that’s celebrated on Helsinki Day, the first baby born on Helsinki Day, whom the city has commemorated since 1965.